# Martian days are moving faster than they used to, and no one knows why

Originally published at: Martian days are moving faster than they used to, and no one knows why | Boing Boing

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Tevye knows.

(Sending a kiddo off to college tomorrow, so this song is living in my head)

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Weird, ain’t it?

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I remember singing “Sunrise Sunset” in choir as a 12 year old, thinking “what a bunch of over-emotional ninnies!” Now the dad-loafer is on the other foot . . .

ETA: (sorry, don’t want to take this off on a tangent). Science!

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I wasn’t theater adjacent, and never saw Fiddler. I wasn’t hip to the song until it was parodied on an ep of That 70’s Show:

Yes, science;

A truly WONDERFUL thing.

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My gods. Why in only 1.5 million years the martian day will be a whole second shorter!

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We’ve all seen ice dancers twirl on the tips of their skates. We know that when they pull in their arms they twirl faster. Pulling in their arms reduces the distance their mass travels in each rotation. Less distance with the same amount of mass means the energy exerted by pulling in their arms has to go somewhere else, so it gets added to their rotational energy. This becomes the rotational speed up we see in the skater. And in that way Mars is no different, other than size. Make the equator a tiny bit smaller, and it has to spin a tiny bit faster. So maybe the core is pushing the poles farther apart, making the equator a little smaller.

Or maybe the Martian core isn’t a perfectly distributed mass. We know that Mars’ rotational axis wobbles. Maybe that means the core is lumpy and just a section of it is molten iron, and the rest is molten rock, and they haven’t mixed together. Iron is much more dense than rock. So if there’s a heavy iron part of the core moving closer to the rotational axis for some reason, that could have the same effect as the skater pulling in their arms, even if we couldn’t see the difference on the outside of the planet.

But if that were the case, what would cause the core to push the heavy lumps inward? Entropy says the heaviest parts should be pushed outward by centripetal force, so some other forces in the core would have to be causing the lumps to migrate inward. Maybe the core is internally spinning in some orientation that’s not at all parallel to the planet’s axis. Or maybe the mantle isn’t uniformly thick, and as the core rotates it gets squished, and when the iron part gets squished inward that causes the speedup.

But because we can see the effect, we know there’s got to be a reason, and so they search for answers.

The fact that we can even measure the Martian core is still absolutely amazing to me, and the idea that people can attempt to answer questions like this is even more amazing.

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Slow news day.

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As a rule gravity is stronger than centrifugal force, which is why objects still fall down even when you drop them at the equator. So for instance inside the earth, convection involves the hot and less dense material rising – the mantle is actually mostly solid, but the pressures involved are enough that it flows anyway. Mars is expected to be solid throughout.

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